High strength, high modulus polyethylene fibers have been prepared from ultrahigh molecular weight polymers by solution spinning and drawing. Such filaments have proven extremely useful for cut-resistant applications, composites, ropes and netting. Conventionally, polymeric solutions have been subjected to spinning to obtain strong polyethylene fibers.
With the advancement of technology, two solution spinning processes were developed. In one solution spinning process, a solution of ultrahigh molecular weight polyethylene (UHMWPE) is prepared at an elevated temperature in a first solvent such as a heavy mineral oil that is essentially non-volatile. This polymer solution is spun and quenched to a gel state essentially without evaporation of the solvent. The solvent is removed from the gel filaments by extraction using another solvent having a boiling point lower than 100° C. The gel filaments containing the second solvent are dried to form xerogel filaments (filaments formed by drying with unhindered shrinkage). Multi-stretching of gel filaments is carried out at three stages: (i) before the extraction of the first solvent, (ii) before evaporating the second solvent and (iii) after drying the filament.
According to a second solution spinning process, a solution of ultrahigh molecular weight polyethylene (UHMWPE) is prepared in a solvent that is volatile. The UHMWPE solution is spun at an elevated temperature, cooled to form gel filaments where the volatile solvent is evaporated and then the filaments are stretched. U.S. Pat. No. 7,147,807 discloses a process for spinning high molecular weight poly (alpha-olefin) (UHMWPO) filament from solution in a volatile solvent with recovery and recycling of the solvent. However, the UHMWPE filament obtained by the process disclosed in U.S. Pat. No. 7,147,207 suffers from drawbacks such as unacceptable crimp, light transmittance, creep and heat resistance.
US Patent Publication No. 20110082262 mentions a composite material prepared by mixing an inorganic substance and an UHMWPE gel solution and processing the solution by a predetermined manufacture process. However, excessive use of inorganic substance cracks or breaks the fibers at an early stage of the process.
Attempts have also been made to prepare high strength and stiffness fibers by orienting the polymer chains in a parallel fashion along the fiber-axis. However, in high performance polyethylene fibers (HP-PE) orientation/extension of the individual molecule is very difficult as these polymer chains are highly flexible and get entangled within themselves and with each other. Furthermore, UHMWPE fibers have a tendency to creep, which makes them inefficient for utilization in long term applications.
In our co-pending application number 1801/MUM/2013, there is provided a process for the preparation of high strength and modulus fibers from a gel composite comprising entangled as well as disentangled UHMWPE. The tensile strength of the resulting fiber ranges from 2.5 to 10 GPa and the tensile modulus from 110 to 300 GPa as a virtue of the dominance of entangled UHMWPE.
In spite of the technological advancements, the conventional processes used for the preparation of fibers from UHMWPE are relatively expensive and produce fibers that have poor morphological and mechanical properties. A need is therefore felt for providing a process for the preparation of fibers having excellent mechanical properties and a gel for the preparation of the fibers.